Changing CapsLock behavior (xkb)

Hello,

I have been trying to change the CapsLock key behavior to work as a
normal shift key (I sometimes accidentally press Caps when I want
shift), and as Caps when Shift_L+Caps (or Control_L+Caps) is pressed.
I tried to modify the group(caps_toggle) option to

xkb_symbols "mycaps_toggle" {
    key <CAPS> {        [  Shift_L,  Caps_Lock ]       };
};

It didn't work. xev reports hat <CAPS> produces Shift_L and Shift-<CAPS>
produces Caps_Lock. Then I added the line 

modifier_maps Lock { Caps_Lock };

No change in behavior. 'xkbcomp :0.0' reports that 
"modifier_map Lock { <CAPS> };", which is not what I wanted. 
I have also tried with type="PC_BREAK" and many, many other
possibilities, and none of them produce the wanted result.
I'm using XFree86 4.3.0 and Gnome 2.6 under Debian/sid. Any help
appreciated.

.jonas.

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